Hard to say. The fact that he was asked to be placed in melee and was added in brawl even years later along with the release of Snake Eater on the 3DS makes me think a good possibility of being on the new one.
On the other hand, the franchise of the game no longer has Snake. Its predominated by Ryker instead on the newest generations. So, in this sense, he might not make it back on there and I could possibly see another reason against his return as well. With a new smash game coming out, they would like to bring in new content I imagine, so having the opportunity to reduce cast in place of other characters would be great. For example, Snake, Sonic, and a couple of the Pokemon are more of special appearance I would say. Oh, look. The cast got reduced to almost thirty if we take out pokemon trainer, lucario, sonic, and snake.